U.S. Pat. No. 3,899,710 issued to Machida et al. on Aug. 12, 1975 describes a color CRT with temperature-responsive color purity magnets attached to the CRT envelope to compensate for beam mislanding on the color phosphor screen caused by thermal expansion of the shadow mask during tube operation. Other expedients such as temperature compensation of the shadow mask, and improved mask material and coating have eliminated the need for such external color purity magnets. However, external magnets are still used to provide corrective or "trimmer" magnetic fields to compensate for non-uniformities in the magnetic field of the deflection yoke positioned on the envelope of the CRT. The need for such "trimmer" magnets is most frequent when tube manufacturers provide CRT-yoke combinations to other original equipment manufacturers (OEM) for use in television receivers or display devices. The OEM may specify a yoke compatible with the receiver which, however, is not optimized for use with the tube on which it is positioned. In such a case, one or more "trimmer" magnets are attached to the outside surface of the tube envelope to compensate for any non-uniformities in the yoke, thereby providing proper register between the electron beams and the color phosphor screen. One type of "trimmer" magnet comprises an extruded strip of plastic filled with ferrite material. Such a trimmer magnet is sold under the name ULTRAMAG 500 and is available from Magnets, Inc. Cincinnati, Oh. The magnet is semi-flexible, meaning that it can be formed to the curved exterior surface of the tube envelope under normal temperature conditions; however, at low temperatures the material is difficult to shape and tends to straighten. The usual method of attaching the magnet to the tube envelope is to apply an adhesive to one side of the magnet; however, the ends of the magnet tend to lift away from the tube envelope during cold weather shipping and storage of the CRT-yoke combination. When this occurs, the free ends of the magnet may be caught on other surfaces during unpacking, handling, or assembly into a receiver or display device, and the "trimmer" magnet may be dislodged or damaged so that the CRT-yoke combination does not operate satisfactorily. The need thus exists for a means of assuring that the "trimmer" magnet remains attached to the CRT-yoke combination.